The present invention relates to a time code arithmetic apparatus for calculating the time code written with the video signal of recording media.
The editing work of the video tape for broadcasting or the nonlinear editing work using the hard disk is carried out accurately based on the absolute address signal recorded in one-to-one relation to the video signal for each frame on the recording-medium (video tape or hard disk). This absolute address signal is called the SMPTE (Society of Motion Picture and Television Engineers)/EBU (European Broadcast Union) time code (hereinafter referred to as the time code) standardized by SMPTE and EBU.
The television transmission system is roughly divided into the NTSC scheme in which a picture for one second configured with 30 images (30 frames) and the PAL and SECAM schemes in which a picture for one second is configured with 25 images (25 frames). The NTSC scheme is employed in Japan, U.S.A. etc., while the PAL and SECAM schemes are used in European countries. The NTSC scheme employs the SMPTE time code reference, and the PAL scheme employs the EBU time code reference.
The unit of the SMPTE/EBU time code is expressed in hours, minutes, seconds and frames, each in two digits for a total of eight digits. The digits of hours, minutes and seconds are counted the same way as the 24-hour clock. The frame digit represents the count 30 for the NTSC scheme, and 25 for the PAL and SECAM schemes, with digits carried up or down to the second digit. Among the TV transmission systems, the NTSC scheme covers 30 frames per second (30 images constituting a picture of one second). Exactly, however, one frame has 33.3 milliseconds, 30 frames per second, and 29.97 Hz per frame (30 Hz: 1000 msec=xHz: 33.3 msecxc3x9730 frames). Therefore, the step of the time code is deviated from the real time, though little by little. This deviation, simply calculated, is 108 frames (3.6 sec) per hour, and the long editing work poses the problem of the deviation from the real time. In the PAL or SECAM scheme, the number of frames is 25 per second (25 images constitute a picture for one second). In these television transmission systems, therefore, the real time is coincident with the time code step.
In the NTSC scheme, two modes are specified as the standard for the time code step.
The first mode is called the drop mode, in which in order to obviate the deviation between the real time and time code step for a long time (one minute or longer), two frames (00 frame and 01 frame, hereinafter referred to as the drop frames) from the start of each minute on the minute except for 0, 10, 20, 30, 40 and 50 minutes are skipped (in other words, the frame 29 is followed by not frame 00 but frame 02) thereby to step the time code. In this mode, two drop frames are skipped 54 times per hour, so that 108 frames are skipped per hour in keeping with the real time. Also, in the drop mode, the picture is continuous, but frame 00 and frame 01 are skipped (absent) as the time code corresponding to the picture in one-to-one relation.
The second mode is called the non-drop mode, which is a method based on the assumption that there is a deviation between the real time and the step of the time code o""clock. In this mode, the time code step is not accompanied by any skip of the frame unlike in the drop mode. Only the non-drop mode is employed for the PAL scheme and the SECAM scheme.
Conventionally, a time code arithmetic apparatus for performing the arithmetic operation in time code of drop mode according to the NTSC scheme (hereinafter referred to as the DF time code o""clock) is disclosed in JP-A-7-203345.
For these two types of DF time code o""clock, there are two methods of add/subtract arithmetic operations. One is, as described in prior art of the time code arithmetic apparatus of JP-A-7-203345, is such that the two input time codes counted in drop mode are converted into the time code in non-drop mode (hereinafter referred to as the NDF time code o""clock), respectively, before add/subtract arithmetic operation, and the NDF time code o""clock constituting the calculation result is reconverted to the DF time code o""clock (hereinafter referred to as the drop mode calculation method 1).
The other method is performed by the time code arithmetic apparatus of JP-A-7-203345, in which two input time codes counted in drop mode are not converted into the NDF time code o""clock but the DF time code o""clock itself is used for calculation with the drop frames added thereto (hereinafter referred to as the drop mode calculation method 2).
Now, the arithmetic relation between the DF time code o""clock and the NDF time code o""clock below.
DFt1: DF time code o""clock providing a reference of add/subtract arithmetic operation.
DFt2, DFt3, DFt4: DF time code o""clock
NDFt: NDF time code hour
If DFt2 less than DFt1 less than DFt3, DFt4, then
xe2x80x83DFt1xe2x88x92DFt2xe2x88x92xcex1=NDFtxe2x80x83xe2x80x83Equation 1
DFt1xe2x88x92NDFtxe2x88x92xcex12=DFt2xe2x80x83xe2x80x83Equation 2
DFt1+NDFt+xcex11=DFt3xe2x80x83xe2x80x83Equation 3
DFt1+DFt2+xcex13=DFt4xe2x80x83xe2x80x83Equation 4
where
xcex1: the number of drop frames skipped from DFt2 o""clock to DFt1 hour
xcex11: the number of drop frames generated upon the lapse of NDFt o""clock from DFt1 o""clock
xcex12: the number of drop frames generated after returning by NDFt time in the case where the time upon the lapse of the time NDFt from DFt2 o""clock is DFt1.
xcex13: two frames in the case where a new drop frame is generated in the calculation process of (time DFt1+DFt2 time) and 0 frame in the case where no new drop frame is generated in the same process.
Equation 1 is the relational equation for calculating the NDF time code o""clock corresponding to the number of frames in real time from the difference of two DF time code o""clock. This equation is used for calculating the duration (real editing time) between the edit start time point and the edit end time point in editing on an editing apparatus.
The value xcex1 in this equation 1 can be calculated by simply subtracting the number of drop frames skipped during the time from 00:00:00.00 o""clock to DFt2 o""clock from the number of drop frames skipped during 00:00:00.00 o""clock to DFt1 o""clock.
Therefore, this xcex1 is the total number of frames dropped in the case where one frame is added each from DFt2 o""clock to DFt1 o""clock.
Also, during the time lapse from Dft2 o""clock to Dft 1 o""clock frame by frame in the case where the result of addition corresponds to a drop frame, +2 frames are skipped and the number of counts is replaced by time data, and then it coincides with the NDFt o""clock.
Equation 2 is the relational equation for calculating the DF time code o""clock obtained when subtracting the NDF time code o""clock representing the number of frames corresponding to an arbitrary real time from DFt1 o""clock. Equation 2 is used, for example, for calculating the DF time code o""clock at the edit start time point before an arbitrary real time after determining the editing end point in editing on an editing apparatus like in equation 1.
The value xcex12 in this equation 2 is theoretically the total number of frames dropped when subtracting frame by frame until the number of frames becomes zero during the time NDFt from DFt1 o""clock.
This xcex12, when an attempt to be made to calculate the DFt2 o""clock from the information of DFt1 o""clock and NDFt o""clock, cannot be easily calculated in view of the fact that a new drop frame may occur in the process of calculation, thereby complicating the calculation.
Equation 3 is the relational equation for calculating the DF time code o""clock when adding the NDF time code o""clock representing the number of frames corresponding to an arbitrary real time from the DFt1 time. A method of using equation 3 is used, when editing on an editing apparatus like in equations 1 and 2, for calculating the DF time code o""clock at the edit end point after an arbitrary real time following the determination of the edit start time.
In this equation 3, xcex11 is theoretically the total number of frames dropped when adding the frames, one by one, for the NDFt o""clock from the DFt1 o""clock.
When an attempt is made to calculate the DFt3 o""clock from the information of DFt1 o""clock and NDFt o""clock, a new drop frame may occur in the process of calculation and therefore this xcex11 is not easy to calculate, and the calculation is complicated.
Equation 4 is the relational equation for calculating the total of the two DF time code o""clock.
The DFt4 o""clock in this equation 4 indicates the drop mode time the DFt2 time after the DFt1 o""clock. Equation 4, like in equations 1, 2, 3, when editing on an editing apparatus, is used for calculating the DF time code o""clock at the edit end point an arbitrary real time after the determination of the edit start time.
In this equation 4, xcex13 is carried up to the minute digit from the second digit when the second digit and the frame digit of DFt1 o""clock is added to the second digit and the frame digit of the DFt2 o""clock and assumes two frames at minutes (one to nine minutes) on the minute not 10 minutes, and there is no generation of a carry up to the minute digit. When in carrying up to the order of ten minutes, as it is 10 minutes on the minute, xcex13 is 0 frame. However, xcex13 assumes four frames only when the second digit and the frame digit of the DFt1 o""clock and the DFt2 o""clock are both 59 seconds 29 frames.
Now, the xe2x80x9ccalculation method 1xe2x80x9d of the drop mode will be explained.
In the case where the DF time code o""clock at the edit end point is calculated when editing only for an arbitrary edit real time after determining the edit start time on an editing apparatus or the like, assume that the DF time code o""clockxc3x97of the edit start point is 1 hour 29 minutes 30 seconds 20 frames and the real edit time is 1 hour 29 minutes 30 seconds and 20 frames (assumed to correspond to the NDF time code o""clock Yxe2x80x2). Then, the correction value of the DF time code o""clockxc3x97into the NDF time code o""clock Xxe2x80x2 is given as
Number of drop frames per hour=108 frames
Number of drop frames per 20 minutes=36 (=2xc3x9718) frames
Number of drop frames per 9 minutes=18 (=9xc3x972) frames
Thus, the correction value is given as
108+36+18=162 frames=5 seconds 12 frames The NDF time code o""clock Xxe2x80x2 to be converted is
1 hour 29 minutes 30 seconds 20 framesxe2x88x925 seconds 12 frames=1 hour 29 minutes 25 seconds 08 frames
This NDF time code o""clock Xxe2x80x2 and NDF time code o""clock Yxe2x80x2 are added as follows
Now, the correction value for converting this NDF time code o""clock again to the DF time code o""clock is
Number of drop frames per two hours=216 (=2xc3x97108) frames
Number of drop frames per 50 minutes=90 (=5xc3x9718) frames
Number of drop frames per 8 minutes=16 (=8xc3x972) frames
Thus, the correction value is given as
216+90+16=322 frames=10 seconds 22 frames The conversion to the DF time code o""clock to be converted is performed in the following manner by adding the correction value to the time code Oxe2x80x2.
2 hours 58 minutes 55 seconds 28 frames+10 seconds 22 frames=2 hours 59 minutes 06 seconds 20 frames
In the process of adding the correction value for this conversion, the carry up from 2 hours 58 minutes 59 seconds 29 frames to 2 hours 59 minutes 00 second 02 frames has occurred, and two new drop frames are generated. Therefore, the edit end point finally calculated is
2 hours 59 minutes 06 seconds 20 frames+2 frames=2 hours 59 minutes 06 seconds 22 frames.
This calculation of the DF time code o""clock is originally considerably complicated in the editing apparatus or the like. In the editing apparatus or the like in initial state, therefore, as described above, the calculation method 1 for the drop mode has often been employed in which the DF time code o""clock is provisionally converted to the NDF time code o""clock, and after calculation, converted into the DF time code o""clock again.
Even in this drop mode calculation method 1, however, the calculation must be repeated and thus become complicated since the recalculation is required when a new drop frame occurs in the process of arithmetic operation of adding/subtracting the correction value for conversion from the NDF time code o""clock to the DF time code o""clock. (In the foregoing example, the carry up from 2 hours 58 minutes 59 seconds 29 frames to 2 hours 59 minutes 00 second 02 frames has occurred, and therefore two frames are added again.)
In order to improve the method of equation 4 described above, publication No. JP 55-032233, corresponding to application No. JP-A-53-103851 (Title of the Invention: Arithmetic Apparatus) has been invented, and further JP-A-7-203345 (Title of the Invention: SMPTE/EBU Time Code Arithmetic Apparatus) was invented which operates equivalently to and with a more simplified configuration than the invention of publication No. JP 55-032233, corresponding to application No. JP-A-53-103851.
This SMPTE/EBU time code arithmetic operation apparatuses both employ the drop mode xe2x80x9ccalculation method 2xe2x80x9d as a method of calculating the DF time code o""clock.
FIG. 11 is a block diagram showing [embodiments] of the laid-open patent publication (hereinafter referred to as the prior art technical publication) of the SMPTE/EBU time code arithmetic apparatus according to JP-A-7-203345 described above (hereinafter referred to as the prior art). Table 1 is a truth table of a first correction instruction circuit 15 described in FIG. 11.
The operation of this prior art will be explained with reference to FIG. 11 and Table 1 as an extraction from the prior art technical publication. The DF time code o""clock X, Y to be added/subtracted are input from input terminals 11, 12, and an add/subtract signal ADD/SUB1 for designating add/subtract operation is input from the input terminal 13. From the arithmetic circuit 14,
Zxe2x80x3xe2x80x2=Xxc2x1Y
is calculated.
In this arithmetic circuit 14, assume a carry up C4 from 10 seconds to minute for add operation, a carry up C5 from minute to 10 minutes, a carry down B4 from minute to 10 seconds for subtraction is B4, and a carry down B5 from 10 minutes to minute. According to the truth table of the first correction instruction circuit of Table 1, the first correction is performed by the first correction instruction circuit 15, so that the P frame and the ADD/SUB2 are output to the arithmetic circuit 17 thereby to accomplish the first correction. In other words,
Zxe2x80x3=Zxe2x80x3xe2x80x2xc2x1P frames
is calculated.
Then, the presence of C4xe2x80x2 and the absence of C5xe2x80x2 are detected in the second correction instruction circuit 21 from the carry up C4xe2x80x2 from 10 seconds to minute and the carry up C5xe2x80x2 from minute to 10 minutes by the calculation for correction in the arithmetic circuit 17, and in this case, the correction of +2 frames is effected in the arithmetic circuit 20. Specifically,
Zxe2x80x2=Zxe2x80x3+2 frames
is calculated.
Next, whether the output Zxe2x80x2 of the arithmetic circuit 20 corresponds to a drop frame or not is detected by the drop frame detection circuit 18, and in the case of corresponding to a drop frame, two frames are subtracted in the arithmetic circuit 19 thereby to effect the third correction. In other words,
Z=Zxe2x80x2xe2x88x922 frames
is calculated, thereby leading to the time code Z as the final result.
In this prior art, when performing the add/subtract operation of the two SMPTE time codes of drop mode, a method is employed for detecting the generation of a new drop frame in the arithmetic process due to the generation of a carry up and a carry down between 10 seconds and 1 minute and between 1 minute and 10 minutes in the arithmetic circuit 14.
For example, the add operation is performed as follows when the time code X is 1 hour 20 minutes 32 seconds 25 frames and the time code Y is 1 hour 30 minutes 29 seconds 15 frames.
In the process, a carry up occurs between 10 seconds and 1 minute in the arithmetic circuit 14, two drop frames occur due to the skip from 2 hours 50 minutes 59 seconds 29 frames to 2 hours 51 minutes 00 second 2 frames. Therefore, the result of adding two frames to the sum 2 hours 51 minutes 02 seconds 10 frames constitutes the final calculation result 2 hours 51 minutes 02 seconds 12 frames.
Also, in the prior art, the hour digit and the minute digit already contain a drop frame from 00 hour 00 minute 00 second 00 frame. In the arithmetic process, therefore, a calculation similar to that for the hour digit and minute digit is possible, so that a new drop frame can be detected in the arithmetic process of the adde/subtract operation between the DF time code o""clock simply by detecting a carry up and a carry down between 10 seconds and 1 minute and between 1 minute and 10 minutes in the add/subtract operation between the second digits or the frame digits.
The prior art described above, however, is considered as a time code arithmetic apparatus for adding/subtracting the two time codes in drop mode according to the NTSC scheme and a SMPTE/EBU time code arithmetic apparatus failing to meet other TV transmission systems including the NDF time code o""clock of PAL scheme or NTSC scheme.
In the method of detecting the generation of a new drop frame in the arithmetic process of two DF time code o""clock, a first correction instruction circuit 15 is provided in case of generation of a drop frame due to the carry up and the carry down between 10 seconds and one minute and between 1 minute and 10 minutes in the add/subtract operation between second digits or frame digits in the first arithmetic process. In order to calculate Zxe2x80x3 from the drop frame P output from the first correction instruction circuit 15 and the time code Zxe2x80x3xe2x80x2 constituting the result of arithmetic operation of the arithmetic circuit 14, the second arithmetic operation is carried out in the arithmetic circuit 17. A second correction instruction circuit 21 is provided in case of generation of a second drop frame in the second arithmetic process.
As described above, in the prior art, correction instruction circuits configured in two stages are included as a means for detecting the generation of a new drop frame, and therefore the size of the time code arithmetic apparatus is increased.
Also, since the arithmetic operation is required for the new drop frame generated after the arithmetic operation, four stages of arithmetic circuits including the arithmetic circuit 14, the arithmetic circuit 17, the arithmetic circuit 20 and the arithmetic circuit 19 are configured, which is another factor for increasing the size of the time code arithmetic apparatus.
The object of the present invention is to provide a time code arithmetic apparatus having a very simple configuration capable of accomplishing the arithmetic operation thus far incapable of being accomplished by the prior art of JP-A-7-203345 (Title of the Invention: SMPTE/EBU time code arithmetic apparatus), in which the mode of the two input time codes need not to be the drop mode, and the arithmetic operation of the time code is carried out by flexibly meeting the requirement of all the television transmission schemes (drop mode/non-drop mode of PAL.SECAM schemes and NTSC scheme).
In order to solve this problem, the present invention is realized based on six basic principles.
The first basic principle relate to the mode of two time codes.
In the prior art, a DF time code o""clock is added/subtracted to and from a reference DF time code o""clock. According to the present invention, in contrast, the NDF code o""clock is added/subtracted.
The original DF time code o""clock is the temporal information in keeping with the real time, in which a drop frame is skipped when counting from 00:00:00.00 o""clock to the real time of DF time code o""clock frame by frame.
If the time is counted frame by frame from 00:00:00.00 o""clock to the DF time code o""clock without skipping a drop frame, the count value represents a NDF time code o""clock.
Based on this principle, the NDF time code o""clock is added/subtracted to and from a reference DFT time code o""clock.
Nevertheless, the drop frame newly occurred in the process of arithmetic operation must be taken into account, and therefore, the NDF time code o""clock corresponding to the total number of drop frames newly generated in this arithmetic process is calculated based on the NDF time code o""clock resulting from the repeated calculation. Then, the DF time code o""clock after the final arithmetic operation is equal to the figure obtained by calculation according to the prior art.
As a result, the time code arithmetic apparatus according to claims 1 to 9 of this invention is configured to add/subtract the NDF time code time to and from the reference DF time code hour.
Also, in the time code arithmetic apparatus according to claims 1 to 9 of the invention, the arithmetic circuit providing the only means for calculating two time code o""clock is adapted to calculate the two input time codes in non-drop mode.
In the case where an input time code constituting a reference of the arithmetic operation is the drop mode, the drop frame newly generated in the process of arithmetic operation is detected in the difference frame number calculation circuit making up means following the arithmetic circuit and an instruction is given for recalculating the time code constituting the result of the arithmetic operation.
In the process, the NDF time code o""clock corresponding to the total number of drop frames detected by the difference frame number calculation means constituting an object of recalculation is added/subtracted to and from the time code making up the result of the arithmetic operation, whereby the time code finally calculated is expressed as a DF time code o""clock.
Now, the concept of calculating calculating two time code o""clock repeatedly will be explained.
The NDF time code o""clock and the DF time code o""clock, when counted frame by frame from 00:00:00.00 o""clock, develops a deviation with time and drop frames are skipped, so that the DF time code o""clock assumes a larger temporal value.
In view of this, this deviation is again add/subtracted to and from the NDF time code o""clock, so that when an arbitrary number of frames is counted from 00:00:00.00 o""clock, the time obtained by adding/subtracting the deviation time to and from the NDF time code o""clock comes to correspond to the DF time code o""clock.
The second basic principle relates to a method of detecting the drop frames newly generated in the process of the arithmetic operation.
By way of explanation, the time code o""clock resulting from the arithmetic operation of adding the DF time code o""clock to the NDF time code o""clock or subtracting the NDF time code o""clock from the DF time code o""clock, i.e., (DF time code o""clockxc2x1NDF time code o""clock) to or from the NDF time code o""clock is hereinafter referred to as the semi-DF time code o""clock.
The total number of drop frames (hereinafter referred to as the drop frame amount) is calculated which has been skipped until the lapse from 00:00:00.00 o""clock to each time code o""clock for both a reference pre-calculation DF time code o""clock Ha and a post-calculation semi-DF time code o""clock Oab.
The calculation of the drop frame amount uses the following equation,
Drop frame amount=(hour digitxc3x97108)+((minute digitxe2x88x92(minute digit/10))xc3x972) framesxe2x80x83xe2x80x83Equation 5
A method is employed for detecting the generation of new drops by detecting the difference of the total (when the difference value is not 0 frame).
This method is different from the complicated prior art detection method in which the drop frames newly generated in the arithmetic process are detected by detecting the carry up and the carry down between 10 seconds and 1 minute and between 1 minute and 10 minutes in the add/subtract operation between second digits and frame digits in the process of arithmetic operation.
The drop frame amount at a reference pre-calculation DF time code o""clock Ha (hereinafter referred to as the pre-calculation drop frame amount Da) is calculated. Similarly, the drop frame amount at a post-calculation semi-DF time code o""clock Oab (hereinafter referred to as the post-calculation drop frame amount) is calculated, and only when the two drop frame amounts fail to be coincident with each other, the generation of a new drop frame is detected.
In the prior art detection method, the drop frames generated newly in the process of arithmetic operation has been fixed to two frames (corresponding to the P frames output from the first correction instruction circuit 15 in FIG. 11, and described in the truth table of Table 1).
According to the first one of the six basic principles of arithmetic operation according to the present invention described above, however, the larger the NDF time code o""clock added/subtracted, the larger the number of drop frames newly generated in the process of arithmetic operation, which number does not assume a fixed value. Therefore, a new detection method has been required.
When adding/subtracting the NDF time code o""clock Hb to and from the reference DF time code o""clock Ha, any difference which may exist between the pre-calculation drop frame amount Da and the post-calculation drop frame amount D indicates that a drop frame(s) has been skipped in the process of adding/subtracting frame by frame the reference DF time code o""clock Ha from 0 frame to the time associated with the total number of frames corresponding to the NDF time code o""clock Hb to be calculated.
When adding/subtracting the NDF time code o""clock Hb to and from the pre-calculation DF time code o""clock Ha in simplified fashion, the post-calculation semi-DF time code o""clock Oab is given by the following relation,
DF time code o""clock Ha (=NDF time code o""clock NdfHa+pre-calculation drop frame amount Da)xc2x1NDF time code o""clock Hb
Semi-DF time code o""clock Oab (=NdfHa+Daxc2x1Hb) It follows that a new drop frame generated in the arithmetic process of adding/subtracting the NDF time code o""clock Hb is not taken into account.
By checking the manner in which the pre-calculation drop frame amount Da inherently existent in the pre-calculation reference DF time code o""clock Ha undergoes a change after arithmetic operation, therefore, the number of frames after the change by the inherently existent pre-calculation drop frame amount Da presents itself in a post-calculation drop frame amount D in view of the fact that the drop frame, if any is existent in the arithmetic process of adding/subtracting the NDF time code o""clock Hb, skipped.
As a result, the drop frames newly generated in the arithmetic process are detected by the change from the pre-calculation drop frame amount Da to the post-calculation drop frame amount D, i.e. the presence or absence of a difference therebetween, while at the same time detecting the number of difference frames.
Now, an explanation will be given below with reference to FIG. 1 for the add operation and FIG. 2 for the subtract operation.
In the case of the add operation, the reference DF time code o""clock is assumed to be 00:16:37.13 o""clock [1] (from equation 5, the pre-calculation drop frame amount [2] is 30 frames), and the NDF time code o""clock to be added is assumed to be 00:02:59.29 o""clock [3] (5399 frames in total), then the first add operation leads to 00:19:37.12 o""clock [4].
In this case, the post-calculation drop frame amount [5] is 36 frames from equation 5, so that the difference between the pre-calculation drop frame amount [2] and the post-calculation drop frame amount [5] before and after the add operation is given as six frame o""clock (00:00:00.06 o""clock [6]).
Since a new drop frame is generated in the carry up from the second digit to the minute digit in the first process of add operation, the repeated add operation is required.
As the second add operation, 00:00:00.06 o""clock [6] corresponding to the difference of the drop frame amount before and after the first add operation is added to the time code 00:19:37.12 o""clock [4] after the first add operation, and in the second add operation, the time code 00:19:37.18 o""clock [7] is led out.
In the second add operation, the post-calculation drop frame amount [8] is 36 frames from equation 5, and there is no difference between the pre-calculation drop frame amount [5] and the post-calculation drop frame amount [8] before and after the second add operation, so that there is no carry up from the second digit to the minute digit in the second process of add operation. In other words, it follows that no new drop frame is generated in the second process of add operation, thereby making it possible to obtain the time code 00:19:37.18 o""clock [9] finally.
The mechanism in which six new drop frames (00:00:00.06 o""clock [6]) are generated in the first add operation described above will be explained below.
In the process of time lapse of the reference DF time code o""clock 00:16:37.13 o""clock [1] frame by frame from 0 frame in the first add operation to the NDF time code o""clock 00:02:59.29 o""clock [3] (5399 frame hours in terms of real frame hours) to be added, the first drop frame is generated upon the lapse from 00:00:22.16 o""clock (676 frame hours in terms of real frame hours) to 00:00:22.17 o""clock (677 frame hours in terms of real frame hours).
After the lapse of 00:00:22.16 hours (676 frame hours in terms of real frame time) from the reference DF time code o""clock 00:16:37.13 o""clock [1], the reference time code o""clock becomes 00:16:59.29 o""clock, while after the lapse of 00:00:22.17 hours (677 frame hours in terms of real frame hours), on the other hand, the reference DF time code o""clock becomes 00:17:00.00. Actually, however, it is 00:17:00.02 o""clock since 00 and 01 frames are drop frames and therefore are skipped.
After that, after the lapse to 00:01:22.15 o""clock (2475 frame hours in terms of real frame time) from 00:01:22.14 o""clock (2474 frame hours in terms of real frame hours), the second drop frame occurs.
After the lapse of 00:01:22.14 hours (2474 frame hours in terms of real frame hours) from the reference DF time code o""clock 00:16:37.13 o""clock [1], the reference time code o""clock becomes 00:17:59.29 o""clock, while after the lapse of 00:01:22.15 hours (2475 frame hours in terms of real frame hours), on the other hand, the reference DF time code o""clock becomes 00:18:00.00. Actually, however, it is 00:18:00.02 o""clock since 00 and 01 frames are drop frames and therefore are skipped.
After that, after the lapse to 00:02:22.13 o""clock (4273 frame hours in terms of real frame hours) from 00:02:22.12 o""clock (4272 frame hours in terms of real frame hours), the third drop frame occurs.
After the lapse of 00:02:22.12 hours (4272 frame hours in terms of real frame hours) from the reference DF time code o""clock 00:16:37.13 o""clock [1], the reference time code o""clock becomes 00:18:59.29 o""clock, while after the lapse of 00:02:22.13 hours (4273 frame hours in terms of real frame hours), on the other hand, the reference DF time code o""clock becomes 00:19:00.00. Actually, however, it is 00:19:00.02 o""clock since 00 and 01 frames are drop frames and therefore are skipped.
In this way, in the time lapse from the reference DF time code of 00:16:37.13 o""clock to the calculation NDF time code of 00:02:59.29 o""clock (corresponding to 5399 frames) frame by frame, three frames (00:17:00:00, 00:18:00.00 and 00:19:00.00) are skipped, and therefore a total of three times of frame drops (two frames of 00, 01 frames for each time) occurs on the minutes (00:17:00.00, 00:18:00.00 and 00:19:00.00). Thus, 6 frames in total are skipped.
Also, by calculating the difference that may occur between the pre-calculation drop frame amount and the post-calculation drop frame amount, the number of frames skipped of the drop frames can be easily calculated in the arithmetic process of adding the NDF time code o""clock to the reference DF time code o""clock.
In the case of subtract operation, assume that the reference DF time code o""clock is 00:16:37.13 o""clock [1] (the pre-calculation drop frame amount [2] is 30 frames from equation 5) and that the NDF time code hours to be subtracted is 00:02:59:29 hours [3] (5399 frame hours in terms of total frame hours). Then, the first subtraction leads to 00:13:37.14 o""clock [4].
In the process, the post-calculation drop frame amount [5] is 24 frames from equation 5, so that the difference between the pre-calculation drop frame amount [2] and the post-calculation drop frame amount [5] before and after the subtract operation is 6 frame hours (00:00:00.06 hours [6]).
Since a new drop frame has occurred in the carry down from the minute digit to the second digit in the first subtract operation, the repeated subtract operation is required.
As the second subtract operation, 00:00:00.06 hours [6] corresponding to the difference of the drop frame amount before and after the first subtract operation is subtracted from the time code 00:13:37.14 o""clock [4] after the first subtract operation, thereby producing the time code 00:13:37.08 o""clock [7] in the second subtract operation.
After this second subtract operation, the post-calculation drop frame amount [8] is 24 frames from equation 5, and there is no difference between the pre-calculation drop frame amount [5] and the post-calculation drop frame amount [8] before and after the second subtract operation, and no carry down occurs from the minute digit to the second digit in the process of the second subtract operation. In other words, no new drop frame has occurred during the second subtract operation. Finally, therefore, the time code 00:13:37.08 o""clock [9] is determined.
Now, the mechanism in which six new drop frames (00:00:00.06 hours [6]) have been generated in the arithmetic process of the first subtract operation as described above will be explained.
While the reference DF time code o""clock 00:16:37.13 o""clock [1] in the first subtract operation is traced back one frame each up to the NDF time code o""clock 00:02:59.29 o""clock [3] (5399 frame hours in real frame hours) subtracted from 0 frame, the first drop frame is generated when 00:00:37.11 o""clock (1121 frame hours in real frame hours) is traced back to 00:00:37.12 o""clock (1122 frame hours in real frame hours).
When the reference DF time code o""clock 00:16:37.13 o""clock [1] is traced back by 00:00:37.11 o""clock (1121 frame hours in real frame hours), the reference DF time code o""clock becomes 00:16:00.02 o""clock, and when it is traced back to 00:00:37.12 o""clock (1122 frame hours in real frame hours), the reference DF time code o""clock is 00:16:00.01 o""clock. Sine 00, 01 frames are drop frames and therefore are skipped, the reference DF time code o""clock becomes 00:15:59.29 o""clock.
After that, when 00:01:37.09 o""clock (2919 frame hours in real frame hours) is traced back to 00:01:37.10 o""clock (2920 frame hours in real frame hours), the second drop frame occurs.
When the reference DF time code o""clock 00:16:37.13 o""clock [1] is traced back by 00:01:37.09 o""clock (2919 frame hours in real frame hours), the reference DF time code o""clock becomes 00:15:00.02 o""clock, and when it is traced back to 00:01:37.10 o""clock (2920 frame hours in real frame hours), the reference DF time code o""clock becomes 00:15:00.01 o""clock. Since 00, 01 frames are drop frames and therefore are skipped, the reference DF time code o""clock becomes 00:14:59.29 o""clock.
After that, when 00:02:37.07 o""clock (4717 frame hours in real frame hours) is traced back to 00:02:37.08 o""clock (4718 frame hours in real frame hours), the third drop frame occurs.
When the reference DF time code o""clock 00:16:37.13 o""clock [1] is traced back to 00:02:37.07 o""clock (4717 frame hours in real frame hours), the reference DF time code o""clock becomes 00:14:00.02 o""clock, and when it is traced back to 00:02:37.08 o""clock (4718 frame hours in real frame hours), the reference DF time code o""clock is 00:14:00.01 o""clock. Since 00, 01 frames are drop frames and therefore are skipped, the reference DF time code o""clock becomes 00:13:59.29 o""clock
In this way, there occur total three times of frame drops (two frames of 00, 01 for each time on the minutes (00:16:00.01, 00:15:00.01 and 00:14:00.01) while the reference DF time code o""clock 00:16:37.13 o""clock [1] is traced back one frame each up to the NDF time code o""clock 00:02:59.29 o""clock [3] (5399 frame hours in real frame hours) subtracted from 0 frame. Therefore, a total of 6 frames are skipped.
Also, due to the fact that the difference has developed between the pre-calculation drop frame amount and the post-calculation drop frame amount, it is possible by calculating the difference to easily determine how many drop frames are skipped in the arithmetic operation of subtracting the NDF time code hours from the reference DF time code o""clock.
Now, an explanation will be given of a method of calculating the number of difference frames between the pre-calculation drop frame amount and the post-calculation drop frame amount.
The add operation and the subtract operation each have two calculation methods.
In the add operation 1, assume that when the NDF time code o""clock Hb to be added is added to the reference DF time code o""clock Ha, the semi-DF time code o""clock Oab providing the result of add operation is larger than or equal to DF time code o""clock Ha before add operation in the value of the time information and that the post-calculation drop frame amount D is larger than or equal to the pre-calculation drop frame amount Da. For example, in such a case as
or in such a case as
Then, the calculation is carried out from the following equation.
xe2x80x83Number of difference frames=post-calculation drop frame amount Dxe2x88x92pre-calculation drop frame amount Daxe2x80x83xe2x80x83Equation 6
In the add operation 2, assume that when the NDF time code o""clock Hb to be added is added to the reference DF time code o""clock Ha, the semi-DF time code o""clock Oab providing the result of add operation is smaller than the DF time code o""clock Ha before add operation in the value of the time information and that the post-calculation drop frame amount D is smaller than or equal to the pre-calculation drop frame amount Da. For example, in such a case as
or in such a case as
Then, the calculation is carried out from the following equation.
Number of difference frames=2592xe2x88x92pre-calculation drop frame amount Da+post-calculation drop frame amount D.xe2x80x83xe2x80x83Equation 7
In equation 7, 2592 frames indicate the total number of frames dropped per 24 hours (108 frames per hourxc3x9724 hours).
In equation 7, the sum of the drop frame amount existing when one frame each is added from the reference DF time code o""clock Ha to 24:00:00.00 (=00:00:00.00) o""clock and the drop frame amount (post-calculation drop frame amount D) existing when adding one frame each time from 00:00:00.00 o""clock to the post-calculation semi-DF time code o""clock Oab is calculated, thereby calculating the difference in the drop frame amount before and after the arithmetic operation.
In the subtract operation 1, assume that when the NDF time code o""clock Hb to be subtracted is subtracted from the reference DF time code o""clock Ha, that the semi-DF time code o""clock Oab providing the result of the subtract operation is smaller than or equal to the DF time code o""clock Ha before the subtract operation in the value of the time information and that the post-calculation drop frame amount D is smaller than or equal to the pre-calculation drop frame amount Da. For example, assume that
or assume that
Then, the calculation is carried out from the following equation.
Number of difference frames=pre-calculation drop frame amount Daxe2x88x92post-calculation drop frame amount D.xe2x80x83xe2x80x83Equation 8
In the subtract operation 2, assume that when the NDF time code o""clock Hb to be subtracted is subtracted from the reference DF time code o""clock Ha, the semi-DF time code o""clock Oab providing the result of the subtract operation is larger than the DF time code o""clock Ha before the subtract operation in the value of the time information and that the post-calculation drop frame amount D is larger than or equal to the pre-calculation drop frame amount Da. For example, assume that
or assume that
Then, the calculation is carried out from the following equation.
Number of difference frames=2592xe2x88x92post-calculation drop frame amount D+pre-calculation drop frame amount Da.xe2x80x83xe2x80x83Equation 9
In equation 9, 2592 frames indicates the total number of frames dropped per 24 hours (108 frames per hourxc3x9724 hours).
In equation 9, the sum of the drop frame amount (=pre-calculation drop frame amount Da) existing when the reference DF time code o""clock Ha is traced back to 00:00:00.00 (=24:00:00.00) o""clock frame by frame and the drop frame amount (=2592xe2x88x92post-calculation drop frame amount D) existing when traced back one frame each time from 00:00:00.00 (=24:00:00.00) o""clock to the post-calculation DF time code o""clock Oab is calculated, thereby calculating the difference in the drop frame amount before and after the arithmetic operation.
In the non-drop mode of PAL.SECAM or NTSC scheme, no drop frame exists, and therefore the difference of the drop frame amount before and after arithmetic operation is not detected.
The third basic principle relates to the recalculation due to the drop frames newly generated.
The arithmetic means (arithmetic circuit) for time code calculation is configured, which unlike the prior art four stages (the arithmetic circuit 14, the arithmetic circuit 17, the arithmetic circuit 20, and the arithmetic circuit 19 in FIG. 11) and only one arithmetic is required in the present invention.
In at least one arithmetic means (arithmetic circuit), the repetitive time code calculation is carried out, and the drop frames newly generated in the arithmetic process are detected by the difference frame number calculation means in later stages.
Then, the selector means A is supplied with the semi-DF time code o""clock Oab after calculation in the arithmetic means and the selector means B with the NDF time code o""clock Nb corresponding to the difference of the drop frame amount before and after the arithmetic operation.
The selector means A is caused by the difference frame number calculation means to select and output the reference semi-DF time code o""clock Oab repetitively calculated, and the selector means B is caused to select and output the NDF time code o""clock Nb to be calculated repetitively.
In the arithmetic means, the two input time codes are recalculated as time codes in non-drop mode by the add/subtract signal Sub without taking any drop frame into account.
In this way, until the difference in the drop frame amount before and after the arithmetic operation is eliminated, the difference frame number calculation means outputs the select information signal ReCalc of the input time code to the selector circuit A a nd the selector circuit B, so that the two time codes individually output from the selector circuit A and the selector circuit B are arithmetically processed repetitively in the arithmetic means.
By doing so, a mechanism is constructed to recalculate the time corresponding to the difference in the drop frame amount before and after the arithmetic operation detected by the method of detecting the newly generated drop frames in the arithmetic process according to the second basic principle described above.
The fourth basic principle is for meeting the requirement of all the TV transmission systems (PAL.SECAM schemes and NTSC scheme in drop mode or non-drop mode) flexibly.
In the time code calculation process, information for calculating the number of frames per second as 30 frames/25 frames in the carry up/carry down of the frame digit is input to the arithmetic means.
Now, an example arithmetic operation of the arithmetic means is shown below.
Let the time code o""clock Ha providing a reference for the arithmetic operation be 00:01:02.13 o""clock, and the time code o""clock Hb to be calculated be 00:00:00.14 o""clock.
Then, in the add operation according to the NTSC scheme,
Since there are 30 frames per second, the carry up from the frame digit to the second digit does not occur.
In the subtract operation according to the NTSC scheme,
Since there are 30 frames per second, the carry down from the second digit to the frame digit occurs, so that the frame digit assumes 29 frames.
In the add operation according to the PAL scheme, on the other hand,
Since there are 25 frames per second, the carry up from the frame digit to the second digit occurs, so. that the frame digit assumes 02 frames.
In the subtract operation according to the PAL scheme,
Since there are 25 frames per second, the carry down from the second digit to the frame digit occurs, so that the frame digit assumes 24 frames.
The next feature is that the difference frame number calculation means is constructed in such a manner as to meet the requirement of drop frames only during the arithmetic operation of the DF time code o""clock in the NTSC scheme.
First, the operation of the difference frame number calculation means will be explained.
The difference frame number calculation means performs the following two operations.
The first operation is such that when calculating the DF time code o""clock according to the NTSC scheme, the difference between the pre-calculation drop frame amount Da and the post-calculation drop frame amount D is determined, and thereby the drop frames newly generated in the arithmetic process are detected.
The second operation is such that upon detection of the drop frames newly generated in the arithmetic process, in order to recalculate the semi-DF time code o""clock from the NDF time code o""clock corresponding to the total number of the particular drop frames during the semi-DF time code hours after arithmetic operation, a signal ReCalc is output to the selector circuit A and the selector circuit B to output the recalculated time code o""clock, while in the case where no drop frame newly generated in the arithmetic process is detected, a signal ReCalc not to recalculate is output to the selector circuit A and the selector circuit B.
In spite of these operations, in the case where the DF time code o""clock of the NTSC scheme is not calculated, i.e. in the case where the NDF time code o""clock is calculated for the PAL.SECOM scheme or the NTSC scheme, the drop frame newly generated in the arithmetic process is not detected in the absence of the drop frame.
As a result, a signal ReCalc not to always recalculate nor to perform the second operation described above is output, so that the arithmetic means normally calculates the time code o""clock in one arithmetic operation, which otherwise might be calculated finally calculated.
The fifth basic principle is for converting the DF time code o""clock of NTSC scheme to the NDF time code o""clock.
The fifth basic principle takes into consideration the fact that the time counted frame by frame without skipping the drop frames from 00:00:00.00 o""clock to the DF time code o""clock corresponds to the NDF time code o""clock, in which case the DF time code o""clock of course indicates the time larger in temporal value than the NDF time code o""clock by an amount corresponding to the skipped drop frames. Thus, by simply subtracting the time corresponding to the drop frame amount of the DF time code o""clock from the DF time code o""clock, the NDF time code o""clock can be calculated.
Let NdfT be the NDF time code o""clock and DfT be the DF time code o""clock before conversion. Then, the drop frame amount DftD of the DF time code o""clock DfT is calculated from equation 5.
Let the time corresponding to the drop frame amount DftD be the NDF time code DfTime, and then
DfTime=00:(DftD/1800):((DftD/30)%60):(DftD %30) o""clockxe2x80x83xe2x80x83Equation 10
(% indicates the remainder in the divide operation) can be used for calculation. Thus, the NDF time code o""clock NdfT to be determined can be calculated from
NdfT=DfTxe2x88x92DfTimexe2x80x83xe2x80x83Equation 11
The sixth basic principle is for converting the NDF time code o""clock of the NTSC scheme into the DF time code o""clock.
The NDF time code o""clock counted from 00:00:00.00 o""clock, as compared with the DF time code having a drop frame counted from the same 00:00:00.00 o""clock, develops a deviation with the lapse of time.
This deviation corresponds to the total number of frames skipped as drop frames when counted from 00:00:00.00 o""clock to the DF time code o""clock.
This time corresponding to the deviation is added to the NDF time code o""clock for conversion to the DF time code o""clock. The number of frames of time to which NDF time code o""clock corresponds as counted in real time can be calculated by arithmetic operation.
Total number of frames=(hour digitxc3x97108000)+(minute digitxc3x971800)+(second digitxc3x9730)+(frame digit)xe2x80x83xe2x80x83Equation 12
Assume, for example, that the NDF time code o""clock is 01:00:00.00. The total number of frames counted from 00:00:00.00 o""clock is 1080000 from equation 12. However, the total number of frames counted from the DF time code o""clock 00:00:00.00 to 01:00:00.00 is given as
(108000xe2x88x92108(number of drop frames per hour)) frames=107892 frames
In other words, the DF time code o""clock is the same real time as the NDF time code o""clock of 01:00:03.18 which is the time code o""clock counted for the remaining 108 frames.
From this, the DF time code o""clock can be calculated by adding the NDF time code o""clock to the drop frame amount based on the assumption that the particular NDF time code o""clock is the DF time code o""clock.
However, the calculation may be impossible by simple addition of the drop frame amount to the NDF time code o""clock. It is in the case where a new drop frame occurs when the drop frame amount is added, in which case the second add operation is required. An example will be explained below with reference to FIG. 3.
Assume that the reference NDF time code o""clock is 00:16:59.13 o""clock [1]. From equation 5, the pre-calculation drop frame amount [2] is 30 frames, which when converted into the time, is 00:00:01.00 o""clock [3].
In this case, the post-calculation drop frame amount [5] is 32 frames from equation 5, and therefore the difference between the pre-calculation drop frame amount [2] and the post-calculation drop frame amount [5] before and after add operation is two frames corresponding to 00:00:00.02 hours [6]. As a result, the carry up occurs from the second digit to the minute digit in the process of the add operation. Thus, the add operation is performed again.
In this case, the post-calculation drop frame amount [8] is 32 frames from equation 5, and therefore there is no difference between the pre-calculation drop frame amount [5] and the post-calculation drop frame amount [8] before and after the add operation, and there is no carry up from the second digit to the minute digit in the second add operation. In other words, due to the absence of drop frames, the final DF time code o""clock 00:17:00.15 o""clock [9] is determined.
In the first add operation described above, an explanation will be given of the fact that the difference of 00:00:00.02 hours [6] has occurred between the pre-calculation drop frame amount [2] and the post-calculation drop frame amount [5].
During the lapse of the time of 00:00:01.00 hours [2] corresponding to the drop frame amount to be added from 00:16:59.13 o""clock [1] constituting the standard NDF time code o""clock in the first add operation, 00:16:59.29 o""clock is realized after the lapse of 00:00:00.16 hours (16 frame hours), while the time is 00:17:00.02 o""clock after the lapse of 00:00:00.17 hours (17 frame hours). Since two drop frames of 00, 01 are skipped, there occurred a difference between the pre-calculation drop frame amount [2] and the post-calculation drop frame amount [5].
In this way, by adding the NDF time code o""clock [3] corresponding to the drop frame amount [2] on the assumption of the DF time code o""clock, to the reference NDF time code o""clock, the NDF time code o""clock can be converted into the DF time code o""clock.
Conversely, for converting 00:17:00.15 o""clock [9] constituting the currently-calculated DF time code o""clock into the NDF code o""clock, the NDF time code o""clock [10] 00:00:01.02 corresponding to the drop frame amount [8] of 32 frames is simply subtracted, and the NDF time code o""clock is calculated as 00:16:59.13 o""clock [11].
The NDF time code o""clock 00:16:59.13 o""clock [11] calculated by conversion from the DF time code o""clock to the NDF time code o""clock as described above is equal to the reference NDF time code o""clock 00:16:59.13 o""clock [1] for converting from the NDF time code o""clock to the DF time code o""clock, and therefore the legitimacy of the method of converting the NDF time code o""clock to the DF time code o""clock can be substantiated.